I'm having similar issues with my 98 YZ400F (same Keihin carb). The owner previous to me opened up the carb from the top of the bowl to the bottom of the slide, removed all the factory sealant and replaced it with loads of RTV. Does anyone know where I can get replacement gaskets, or some sort of fix for this?
My bike will not idle and is a problem to get started. Everything from mid to full throttle runs like a bat out of hell. The plate seal is good, slide is good.